| sci.electronics.repair@googlegroups.com | Google Groups |  |
| Unsure why you received this message? You previously subscribed to digests from this group, but we haven't been sending them for a while. We fixed that, but if you don't want to get these messages, send an email to sci.electronics.repair+unsubscribe@googlegroups.com. |
- ground plan antenna design and height. - 5 Updates
- Old Singer Sewing Machine - No Variable Speed - 1 Update
- Sharp fax machine - changing the lithium battery (yes, I know) - 4 Updates
| captainvideo462009@gmail.com: Nov 05 08:57PM -0800 I'm planning on building a 10 meter ground plane antenna out of PVC pipe and #12 wire radials drooping about 40 degrees. This will be mounted on my roof on a tripod and mast, with the radials also serving as guy wires. The ARRL antenna book mentions that a ground plane antenna should be mounted at least one half wavelength above "ground". I know that this sounds like a stupid question but I have to ask: for this example do I consider the roof, which is more than 5 meters above ground level as "ground" or do I need to at least 5 meters above the roof. I would like to secure the radials, (guy wires) to my roof, but with the antenna at 5 meters high my droop angle will be off and then I can't guarantee a 50 ohm match. The house is wood frame. Thanks for any advice. Lenny |
| Jeff Liebermann <jeffl@cruzio.com>: Nov 05 10:39PM -0800 On Wed, 5 Nov 2014 20:57:12 -0800 (PST), captainvideo462009@gmail.com wrote: I'll pretend that this has something to do with "repair". >I'm planning on building a 10 meter ground plane antenna out of PVC pipe and #12 wire radials drooping about 40 degrees. This will be mounted on my roof on a tripod and mast, with the radials also serving as guy wires. The ARRL antenna book mentions that a ground plane antenna should be mounted at least one half wavelength above "ground". I know that this sounds like a stupid question but I have to ask: for this example do I consider the roof, which is more than 5 meters above ground level as "ground" or do I need to at least 5 meters above the roof. I would like to secure the radials, (guy wires) to my roof, but with the antenna at 5 meters high my droop angle will be off and then I can't guarantee a 50 ohm match. The house is wood frame. Thanks for any advice. Lenny Don't worry about the exact angle of the ground radial drop. If the fell against the coax cable, the antenna would be about 70 ohms. If they stuck straight out and were perpendicular to the coax, about 35 ohms. If at a 45 downward droop, 50 ohms. The VSWR and mismatch loss for these are: 70 ohms = 1.4:1 = 0.12 dB 50 ohms = 1:1 = 0.0 dB 35 ohms = 1.4:1 = 0.12 dB I think you can handle 0.12 dB of loss quite easily and 1.4:1 VSWR is not going to blow up your 10 meter transmitter. There also will be little effect to the vertical antenna pattern as the vertical beamwidth is a rather large 80 degrees. If you add a 5 meter pole to the base of the ground plane, then your radials will be almost covering the coax cable feed and you'll have something closer to a 70 ohm antenna. Instead of trying to fix that, just call it a "coaxial antenna" instead of a "ground plane". End of that problem. I'm not sure what part of your house to consider as ground level. It can be anywhere between the roof and the ground, depending on how much metal you have in the roof, walls, ceiling, slab, etc. If you have foil backed insulation in the attic, use that ceiling as the ground. If you're house is miserably insulated and effectively RF transparent, use the earth ground level. I can't be more helpful without a description of the building and ground. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Pat <pat@nospam.us>: Nov 06 08:40AM -0500 On Wed, 05 Nov 2014 22:39:41 -0800, Jeff Liebermann <jeffl@cruzio.com> wrote: >If you're house is miserably insulated and effectively RF transparent, >use the earth ground level. I can't be more helpful without a >description of the building and ground. Are these radials cut to length (perhaps with insulators) or are they many wavelengths long? Coaxial antennas usually have the portion of the shield that goes back over the feed line cut to a quarter wavelength. And radials on typical VHF/UHF ground planes are usually cut to around a quarter wavelength. I would think adding length to make them double as guy wires would have a significant effect. I am not an expert in this area so I am not critisizing ...just curious. Pat |
| captainvideo462009@gmail.com: Nov 06 07:03AM -0800 > I'm planning on building a 10 meter ground plane antenna out of PVC pipe and #12 wire radials drooping about 40 degrees. This will be mounted on my roof on a tripod and mast, with the radials also serving as guy wires. The ARRL antenna book mentions that a ground plane antenna should be mounted at least one half wavelength above "ground". I know that this sounds like a stupid question but I have to ask: for this example do I consider the roof, which is more than 5 meters above ground level as "ground" or do I need to at least 5 meters above the roof. I would like to secure the radials, (guy wires) to my roof, but with the antenna at 5 meters high my droop angle will be off and then I can't guarantee a 50 ohm match. The house is wood frame. Thanks for any advice. Lenny Typically when building a ground plane antenna (according to the ARRL books), you would make the "ground" radials, (usually there are at least 4 of them) five percent longer than .25 wavelength. I don't know why that is but it's mentioned in the books. And yes at the end of those radials you would put insulators. The other end of the insulator,( I use a piece of Lexan with two holes drilled in it) becomes the "guy wire". It would be tied off if possible at the 40 degree or so angle I previously mentioned thereby making the entire length double as a radial and a guy wire. I already have another ground plane antenna I built several years ago which is mounted on the roof for my business band base station. That operates in the the 40 MHZ range and although naturally shorter is still nowhere near .50 wavelength above the roof but it has always seemed to have decent coverage. This all just got me wondering though. To answer your question about the house Jeff, there is no foil insulation, non metal roof, and unless you count the copper plumbing and electrical wiring as having a significant effect on this scenario there's not much else that I could see that could be factored in. I do have an SWR meter, however except by extrapolating the information I would need by looking at the SWR at the operating frequency I don't have an easy way to measure feed line or antenna impedance. Lenny |
| Jeff Liebermann <jeffl@cruzio.com>: Nov 06 08:45AM -0800 >Are these radials cut to length (perhaps with insulators) or are they >many wavelengths long? Cut to length for about 1/4 wavelength at 10 meters or about 2.5 meters long. >Coaxial antennas usually have the portion of >the shield that goes back over the feed line cut to a quarter >wavelength. If you actually test such a coaxial antenna, you'll probably find that it doesn't quite work. If the braid is too close to the coax cable, bad things happen. That's why they usually have a small spacer. Typical 2.4GHz coaxial antenna. <http://802.11junk.com/jeffl/antennas/coaxial/coax-ant.jpg> If you look carefully, you'll notice that the length of the driven element (on the left) is longer coax "sleeve" element. It's not really symmetrical. >And radials on typical VHF/UHF ground planes are usually >cut to around a quarter wavelength. I would think adding length to >make them double as guy wires would have a significant effect. Correct. I didn't notice that problem in the original question. I assume that the ground radial wires would be cut to the proper length and extended to the roof line with insulating nylon rope. I was only concerned about their droop angle. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| captainvideo462009@gmail.com: Nov 05 09:20PM -0800 > any suggestions. > thanks! > -Pete My wife has a 35 year old Singer with the same type of speed control. Hers developed the same problem several years ago and increasing the disc tension slightly fixed the problem. If yours is unserviceable how about an old time sewing machine store? We have a guy around here that's been in the vacuum cleaner business since Columbus came over. He has a supply of old vacuums from day one. Perhaps you might be able to find someone like that who may have one of these just collecting dust. I would have to agree with Jeff about not using a PWM type of speed control. For the same reason I never put one on my 1953 Lionel train set. Lenny |
| Peabody <waybackNO584SPAM44@yahoo.com>: Nov 05 02:44PM -0600 I know this is a long shot, but someone may know. I have a Sharp model UX- D1200SE fax machine which actually works well. But I only need it a couple times a year, so I don't leave it plugged in. It has a lithium battery that keeps time and the settings, but the manual says it must be replaced by an authorized service center. I called Sharp, and they repeated that requirement, but said they have no service center where I live, so I would have to send in the machine to them to get the battery changed. They refused to tell me how to replace the battery. Right. I've looked over the machine carefully, and don't see any likely entry for this. And I can't find anything about this through Google. Any info or suggestions would be appreciated. |
| Phil Allison <pallison49@gmail.com>: Nov 05 03:34PM -0800 Peabody wrote: > I've looked over the machine carefully, and don't see any likely entry for > this. And I can't find anything about this through Google. > Any info or suggestions would be appreciated. ** Many Lithium cells are mounted on the main PCB, held by solder links that are attached to the cells. For example; http://www.henlimax.com/imageRepository/239b1aa8-4668-45f2-95db-1f1af80ef215.gif They normally last anywhere from 10 to 20 years. So, you have to open the machine, find the cell and then get one like it. Remove the old one and fit the new one with a soldering operation. ... Phil |
| "William Sommerwerck" <grizzledgeezer@comcast.net>: Nov 05 03:35PM -0800 The lithium battery is usually a coin cell, so-called because it's about the size and shape of a coin. It's almost universal in personal computers, to retain the BIOS settings when the machine is unplugged. My JVC and Yamaha hall synthesizers also have them to retain user settings. It's sometimes installed in a socket, but most-often is directly soldered into the board. It should be plainly visible. If you're handy with a soldering iron, you should have no trouble replacing it. You might want to purchase and solder in a socket, so you won't have to unsolder anything again. |
| John Robertson <spam@flippers.com>: Nov 05 06:04PM -0800 On 11/05/2014, 12:44 PM, Peabody wrote: > I've looked over the machine carefully, and don't see any likely entry for > this. And I can't find anything about this through Google. > Any info or suggestions would be appreciated. If you don't want to lose the settings or the machine has one of those battery suicide software (when the battery dies the CMOS loses serial number or some such and you can't revive the device) - look up Capcom Suicide Battery as an example. The best way to replace the battery is with the power on, or a second power supply providing power to the CMOS device while you replace the battery. As others have said a socket isn't a bad idea here, however get a good quality one that has plenty of grip on the battery. Unsoldering a battery while the power is on requires an ISOLATED tip iron. A Butane soldering tool works well for example. You don't want the tip grounded or you will short out the battery while soldering it in. If your tip retains heat well you can try soldering a second battery across the solder tabs of the original by unplugging the soldering iron just before you try to solder the wires. Turning it off won't break the ground connection to the tip, you MUST unplug it! I much prefer the Butane soldering tool for this sort of job though. John :-#)# -- (Please post followups or tech inquiries to the newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
| You received this digest because you're subscribed to updates for this group. You can change your settings on the group membership page. To unsubscribe from this group and stop receiving emails from it send an email to sci.electronics.repair+unsubscribe@googlegroups.com. |
No Response to "Digest for sci.electronics.repair@googlegroups.com - 10 updates in 3 topics"
Post a Comment